1. Lipoproteins
Seminar No. 2
- Chapter 13 -

2. Lipids of Blood Plasma Lipid Plasma concentration Cholesterol (C+CE)*
Phospholipids
Triacylglycerols
Free fatty acids
3-5 mmol/l
~ 3 mmol/l
~ 1.5 mmol/l
~ 0.5 mmol/l
* C = free cholesterol, CE = cholesteryl-esters

3. Q. 1 (p. 78) Which natural tensides participate in micelle formation
in intestine (GIT) ?
What is a tenside?

4. A. 1 Tenside is compound with polar head and non-polar tail(s)
Type
Origine
Bile acids
2-Acylglycerol
FFA anions
Phospholipids
anionic
non-ionic
amphoteric
from cholesterol in liver
hydrolysis of TAG in GIT
food
They all together make a micelle which enters enterocyte

5. In which form are FFA transported in blood?
Q. 2 (p. 78)
In which form are FFA transported in blood?

6. A. 2 FFA are non-polar species, insoluble in water.
They are bound to albumin, which is the main transport protein in plasma.

7. Lipoprotein particle
Polar surface monolayer contact with aqueous environment
Non-polar core completely separated from aqueous environment

8. Components of Surface Layer
Pictogram
Name ?

9. Components of Surface Layer
Pictogram
Name
phospholipid
free cholesterol
(apo)protein

10. Draw a general structure of phospholipid or phosphatidylcholine

11. Structure of phospholipid
phosphatidylcholine (lecithine)

12. Structure of cholesterol
27 carbon atoms
1 hydroxyl (C3)
1 double bond (C5)
the only polar group

13. Non-polar core of lipoprotein
Pictogram
Name ?

14. Non-polar core of lipoprotein
Pictogram
Name
triacylglycerol
cholesteryl ester

15. Draw a structure of TAG

16. triacylglycerol (TAG)

17. Plasma lipoproteins: Density vs. Composition
Class
Density (g/ml)
Proteins (%)
TAG (%) CM
VLDL
LDL
HDL
0.90
0.95
1.05
1.20 2 9 21 50 84 54 11 4

18. Electrophoretic separation of lipoproteins
see the scheme on p. 73, bottom right side Q.
Why are CM located at the origine (start)?

19. A. CM do not move in electric field
they are predominatly non-polar species
they have minimal value of electric charge
only 2 % of proteins

20. The Composition of Lipoproteins
Features to remember
Lipoprotein
Main component
Chylomicrons
VLDL
LDL
HDL
~ 85 % TAG
~ 50 % TAG
~ 45 % cholesterol
~ 50 % proteins

21. Functions of apoproteins
Structural components of surface monolayer
Activators of some enzymes (LPL, LCAT)
Assist in remodelling (lipid transfer between lipoprot.)
Ligands for specific receptors in tissues

22. Transport functions of lipoproteins
Class
Origine
Transport CM
VLDL
LDL
HDL
enterocyte
liver
plasma
exogenous TAG from GIT to peripheral tissues
endogenous TAG from liver to periph. tissues
cholesteryl esters to peripheral tissues
cholesterol from tissues to liver

23. Enzymes in lipoprotein metabolism
Substrates
Reaction
Location
LPL HL
LCAT
TAG of CM, VLDL
TAG of IDL, HDL
cholesterol + lecithin
hydrolysis
esterification
capillaries
liver
HDL
LPL = lipoprotein lipase
HL = hepatic lipase
LCAT = lecithin cholesterol acyltransferase

24. Write the equation of reaction catalyzed by LPL

25. LPL reaction
TAG H2O  glycerol + 3 FFA
LPL

26. Write the equation of reaction catalyzed by LCAT (lecithin cholesterol acyltransferase)
What is acyl?

27. A.

28. LCAT reaction lyso = 2-deacyl
cholesterol + lecithin  cholesteryl ester + lysolecithin
lyso = 2-deacyl

29. cholesterol
lecithin
LCAT
cholesteryl ester
lysolecithin

30. Metabolism of chymomicrons (CM)
CM are produced in enterocytes, apo B-48
They carry dietary TAG and CE to periph. tissues
In plasma, CM receive apo E and apo C-II from HDL
Apo C-II activates lipoprotein lipase (LPL)
LPL is attached to capillary surface in adipose, cardiac and muscle tissues
TAG are hydrolysed, apo C-II is returned to HDL
CM particles begin to shrink – remnants
Remnants bind to apo E receptors in liver, where they are hydrolytically degraded in lysosomes

31. What will be result of deficient synthesis of apo B-48?
Q.5 (p. 78)
What will be result of deficient synthesis of apo B-48?

32. No CM will be produced, dietary fat remains in stool (steatorrhoea)

33. Metabolism of VLDL
VLDL are made in liver, they transport endogenous TAG to periph. tissues
In plasma they take apo C-II from HDL (LPL activ.)
TAG are removed by LPL action – VLDL become smaller and more densed = IDL
IDL take some CE from circulating HDL
IDL are transformed into LDL by hepatic lipase

34. Q. (p. 76)
Name some dietary factors which may affect the synthesis of VLDL in the liver.

35. Food rich in lipids (fat) and saccharides (sugars)

36. How are utilized fatty acids released by LPL?
Q. (p. 76)
How are utilized fatty acids released by LPL?

37. A. Depending on energy status in tissues FFA are:
either utilized for energy (β-oxidation  acetyl-CoA  CAC)
or substrates for TAG synthesis (making energy reserves)

38. Three pathways of LDL
LDL provide cholesterol to peripheral tissues via LDL receptors
The rest of LDL is taken up by liver and degraded
Small amount of LDL (chemically modified by oxidative stress) enters to some cells (endothelial) by non-specific endocytosis and alters them to „foam cells“

39. Metabolism of HDL HDL particles are made in liver
Nascent HDL are disc-shaped (bilayer of PL + proteins)
HDL take free cholesterol (C) from cell membranes
Once C is taken up, it is esterified by LCAT
After this process HDL becomes spherical
Spherical HDL are taken up by liver and CE are degraded

40. Cellular uptake of LDL LDL receptors are in clathrin-coated pits
After binding, LDL+receptor are internalized by endocytosis
Vesicle loses its clathrin coat and becomes endosome
Receptor is removed and recycled
LDL is hydrolyzed after fusing with lysosome
Free cholesterol is released to make cholesterol pool

41. Intracellular cholesterol
Free cholesterol is immediately esterified by ACAT* (storage)
Small amounf of C is incorporated into cell membrane
Some C is converted into hormones (in some tissues)
Some C is converted into bile acids (in liver)
* acyl-CoA cholesterol acyltransferase

42. Intracellular cholesterol regulates three processes
Decreases activity of HMG-CoA reductase (= synthesis of cholesterol)
Decreases synthesis of new LDL receptors (to block intake of LDL)
Enhances activity of ACAT (to help making storage)

43. The Balance of Cholesterol
Input into body g/day
Output from body g/day
food
biosynthesis in body
Total:
0.5 g
1.0 g
1.5 g
coprostanol (stool)
bile acids (stool)
sebum, skin etc.
0.8 g
0.2 g

44. Which food is the main source of cholesterol?Q.
Which food is the main source of cholesterol?

45. A. only animal fats (including fish)
lard, butter, bacon, egg yolk, mayonnaise, fat meat, fat cheese
plant oils and margarines are cholesterol free